1. Field of the Invention
The present invention relates to a liquid transporting apparatus which transports a liquid.
2. Description of the Related Art
Various liquid transporting apparatuses which transport a liquid to a predetermined position by applying pressure to the liquid, and an ink-jet head in which ink is transported to nozzles and discharged from the nozzles on to an object for discharge such as a recording paper are hitherto known. Among the ink-jet heads, an ink-jet head disclosed in U.S. Patent Application Publication No. U.S. 2003/107622 A1 (FIGS. 6 to 8) corresponding to Japanese Patent Application Laid-open Publication No. 2004-166463, includes a channel unit (cavity plate) in which a plurality of pressure chambers which is long in one direction and communicating with the nozzles are formed, and a piezoelectric actuator which applies pressure for causing an ink to be discharged from the nozzles by changing a volume of the pressure chambers.
Moreover, the piezoelectric actuator of this ink-jet head includes a plurality of piezoelectric sheets made of lead zirconate titanate (PZT) and arranged to cover the pressure chambers, and individual electrodes (drive electrodes) and common electrodes which are arranged alternately between the piezoelectric sheets. The individual electrodes and the common electrodes are formed in areas respectively overlapping the pressure chambers as viewed from a direction orthogonal to a plane of the piezoelectric sheets, in the form of a ring around a circumference of each of the pressure chambers. The piezoelectric actuator has a construction capable of performing a so-called ejection at suction timing in which once the piezoelectric actuator increases the volume of the pressure chambers to draw the liquid into the pressure chambers, then the piezoelectric actuator decreases the volume of the pressure chambers to apply a substantial amount of pressure to the liquid.
In other words, when a drive voltage is applied to the individual electrodes while the common electrodes are kept at a ground potential, portions of the piezoelectric sheets having the shape of a ring along the circumference of each of the pressure chambers, which are sandwiched between the individual electrodes and the common electrodes are contracted in a direction parallel to the planes of the piezoelectric sheets. As a result, the plurality of piezoelectric sheets are deformed to project toward a side opposite to one of the pressure chambers, thereby increasing the volume inside the pressure chamber and generating a pressure wave inside the pressure chamber. Further, when the drive voltage applied to the individual electrodes is stopped at a timing when the pressure wave in the pressure chamber changes to positive, the piezoelectric sheets are restored to the original shape, thereby reducing the volume inside the pressure chamber. However, at this time, the pressure wave generated with the increase in the volume of the pressure chamber and the pressure wave generated with the restoration of the piezoelectric sheet are combined and a substantial pressure is applied to the ink. Therefore, the piezoelectric actuator of this ink-jet head is capable of applying a substantial pressure to the ink with a comparatively low drive voltage. Accordingly, a drive efficiency of the piezoelectric actuator is improved. Moreover, the actuator is structured such that an electric field is made to act on a piezoelectric layer by applying the drive voltage to the individual electrodes only at a timing of ink discharge, and the electric field is not applied to the piezoelectric layer at timing other than the timing of ink-discharge. Therefore, polarization deterioration hardly occurs in the piezoelectric layer, and accordingly the durability of the actuator is improved.